Jennifer Lopez -- Drunk Driver Nailed ... That's How the D.A. Rolls

The guy who smashed into Jennifer Lopez's brand new Rolls-Royce was bombed -- nearly twice the legal limit -- and now could face time behind bars ... according to prosecutors.

The L.A. County D.A.'s office is charging Robert John Reitz with two misdemeanor counts of DUI for the September rear-ender on Pacific Coast Highway -- and they say his blood alcohol content was an astonishing .15.

You'll recall JLo and her pal Leah Remini were cruising in Jennifer's Rolls at the time of the accident. They posted a pic of themselves looking fabulous ... just seconds before Reitz hit them and fled the scene.

Reitz faces 6 months in jail and a $1,000 fine if convicted.